This application claims the priority of application no. 102 42 860.3-25 filed in Germany on Sep. 14, 2002, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a collapsible bridge; that is, a portable bridge for mobile use.
From German Patent Document DE 195 10 582 A1 (corresponding U.S. Pat. No. 5,724,691), a portable bridge is known whose track girders are force-lockingly connected by means of transverse girders. In this case, a transverse girder forms a part of the lower chord. Furthermore, roadway planks are provided which are aligned in the longitudinal direction of the bridge and are force-lockingly connected with the transverse girders. The track girders each comprise two truss planes of diagonal struts, the lower chord and the upper chord. These components forming the track girder are in each case mutually connected by means of connections which can be released again.
German Patent Document DE 2 250 013 A1 (corresponding GB Patent No. 1 405 146) describes a portable bridge whose track girders have a triangular cross-section. A chord profile exists at each triangulation point. The two base sides of the track girders each consist of a so-called quadrilateral beam. This is a frame-type carrying structure with additional diagonal struts. The track girders cannot be changed with respect to their geometry. The transverse girders connected with the track girders are spliced at the track girders.
Portable bridges should be transported in a cost-effective manner with expenditures which are as low as possible. For this purpose, two characteristics are particularly important:                1. A low requirement with respect to transport space,        2 a low weight.        
This applies particularly when the bridges have to be transported as air freight over large distances.
In order to implement light-weight bridge structures, the dimensions, mainly the height of the bending members of the carrying construction, should be as high as possible, and the used materials should be as light, firm and rigid as possible.
In order to implement bridge structures having a transport space requirement which is as low as possible, the components should be as small as possible and mainly should be easily stackable.
A conflict exists here between these preferred design features which is to be solved by means of the present invention.
It is therefore an object of the invention to provide a bridge which provide at least one or more of the following advantages:                the bearing bending members can be selected to be as high as possible;        the use of light-weight, firm and rigid materials, particularly fiber materials, can take place in an effective manner;        the bridge can be transported with a space requirement which is as low as possible; and        the bridge can rapidly be built up and taken down.        
This object is achieved according to certain preferred embodiments of the invention by providing a collapsible bridge having two track girders which are constructed as truss girders with a triangular cross-section, wherein a chord profile is provided at each triangulation point, and wherein two corners of the triangular cross-section are situated at the same level, and the third corner is situated above the latter, wherein, in each case, between one of the lower triangulation points and the upper triangulation point, a truss plane is formed comprising diagonal struts, the lower chord and the upper chord, wherein lower and upper truss nodes respectively are formed at the points of the connection of two diagonal struts and a lower chord and an upper chord respectively.
The bridge according to certain preferred embodiments of the invention is constructed as follows:                It comprises two track girders which are constructed as truss carries with a triangular cross-section, two corners of the triangular cross-section being situated at the same level, and the third corner being above the latter, in which case a truss plane comprising diagonal struts, a lower and an upper chord is formed in each case between one of the lower triangulation points and the upper triangulation point of the track girder cross-section, lower and upper truss nodes respectively being formed at the points of the connection of two diagonal struts and a lower chord and an upper chord respectively;        the two track girders are force-lockingly connected by transverse girders;        roadway planks aligned in the longitudinal direction of the bridge are provided which are force-lockingly connected with the transverse girders;        the transverse girders are fitted completely through the track girders and are force-lockingly connected with the latter, so that the transverse girders fix the spacing of the two truss planes on the underside of the track girder as well as the track girders with respect to one another. In this case, the transverse girders rest on the lower nodes of the two truss planes of a track girder and are force-lockingly connected with the latter; and        at the upper point of triangulation of the track girder cross-section, the two truss planes of a track girder are connected by means of a hinge, so that the track girders can be folded together when the bridge is taken down.        
A bridge constructed in this manner has the following advantages:                Because the bridge is subdivided into individual flat and easily stackable elements, it requires little transport space.        Because the bridge is subdivided into individual predominantly one- or two-dimensionally stressed elements, the prerequisites are provided for the use of fiber composites, and low weights can therefore be achieved.        
The described construction of the track girders provides the prerequisite for a simple collapsing of the track girders. The volume of the track girders is considerably reduced by the folding-together of the two truss planes for the transport. The static connection of each of the two truss planes is not disconnected during the collapsing. The static connection of the two truss planes is optimally implemented with respect to weight by means of unreleasable connections. Thus, there are no loose connection elements which could easily be lost in the terrain during rain, ice and snow and in darkness. The setting-up of the unfolded form of the track girder required for the use from the volume-saving folded-together form can be achieved with a minimal expenditure of time without any supplementary devices.
The transverse girders and the roadway planks are no primary structures; that is, their failure does not necessarily cause the failure of the bridge as a whole.
The transverse girders, roadway planks and collision aids can also be exchanged when the bridge is already constructed.
As a result of its low weight, the bridge requires correspondingly little counterweight when it is laid.
Advantageously, the track girders are coupled together of one or more track girder sections in the longitudinal direction of the bridge. At their ends, the track girders are closed off by means of end pieces. These may simultaneously be used as bridge bearings.
Typical spans of the bridge according to the invention are in the range of up to approximately 30 m.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.